21st century California drought risk linked to model fidelity of the El Ni\xf1o teleconnection

Robert J Allen,Ray G Anderson

doi:10.1038/s41612-018-0032-x

Abstract

Greenhouse gas induced climate change is expected to lead to negative hydrological impacts for southwestern North America, including California (CA). This includes a decrease in the amount and frequency of precipitation, reductions in Sierra snow pack, and an increase in evapotranspiration, all of which imply a decline in surface water availability, and an increase in drought and stress on water resources. However, a recent study showed the importance of tropical Pacific sea surface temperature (SST) warming and an El Niño Southern Oscillation (ENSO)-like teleconnection in driving an increase in CA precipitation through the 21st century, particularly during winter (DJF). Here, we extend this prior work and show wetter (drier) CA conditions, based on several drought metrics, are associated with an El Niño (La Niña)-like SST pattern. Models that better simulate the observed ENSO-CA precipitation teleconnection also better simulate the ENSO-CA drought relationships, and yield negligible change in the risk of 21st century CA drought, primarily due to wetting during winter. Seasonally, however, CA drought risk is projected to increase during the non-winter months, particularly in the models that poorly simulate the observed teleconnection. Thus, future projections of CA drought are dependent on model fidelity of the El Niño teleconnection. As opposed to focusing on adapting to less water, models that better simulate the teleconnection imply adaptation measures focused on smoothing seasonal differences for affected agricultural, terrestrial, and aquatic systems, as well as effectively capturing enhanced winter runoff.

Highlights

Not all El Niño (La Niña) winters are wetter than normal since other factors contribute to CA hydrological variations, and some evidence suggests the El Niño-CA precipitation relationship may not be stationary through time,[40,41,42] this teleconnection represents a reasonably strong pathway by which CA precipitation variations occur
We note that El Niño influence on California precipitation is strongest during late winter, and is stronger in the south than the north.[43]
Building off previous work,[27] CMIP5 models that better simulate the observed correlation between CA precipitation and El Niño interannual variability yield larger and more consistent increases in California precipitation, surface water availability and runoff under global warming, with relatively small changes in soil moisture ( SMB)

Summary

Introduction

In response to anthropogenic climate change, climate models from the Coupled Model Intercomparison Project (CMIP) version 3 and 5 indicate a likely transition to a more arid climate over many land areas,[1] resulting in increased frequency and intensity of drought.[2,3] Severe and widespread drought during this century are of particular concern for southwestern North America, including California (CA).[4,5,6,7,8] This drying is a consequence of reduced precipitation in the subtropics, and a poleward expansion of the subtropical dry zones.[9,10,11,12,13] in addition to reduced precipitation, warmer temperatures will lead to an increase in evapotranspiration[3] and a decrease in mountain snow mass.[6]. Future drought risk in southwestern North America may even exceed that during the driest centuries of the Medieval Climate Anomaly.[15,16]

Methods

Results

Conclusion